The present invention relates to a visibility adjusting method and an apparatus for adjusting a driver's forward visibility by providing a lower end of a windshield with a visibility adjusting section.
Conventionally, there is known a visibility adjusting method of a vehicle in which a lower end of a windshield is shielded, and the forward visibility is adjusted in accordance with a running state, thereby enhancing a forward visibility at driving as disclosed in Japanese Patent Application Laid-Open No. 2000-211355 for example.
In such a conventional visibility adjusting method, an actual vehicle speed and a distance between vehicles are detected, and these values are compared with corresponding values of a calculation method so that the visibility is limited when running on an expressway to prevent fatigue and sleepiness, and sufficient visibility is secured during medium and low speed running to prevent the driver from overlooking an obstacle existing immediately in front of the vehicle.
That is, if the visibility immediately in front of the vehicle is excessively excellent, the driver's nerve is worn and fatigue is increased. In order to prevent this, the height of the lower end of the windshield is changed in accordance with situation, thereby limiting the visible area.
In the conventional visibility adjusting method of a vehicle, however, a parting line of an upper end edge which shields the lower end of the windshield extends straightly in a vehicle-width direction. Therefore, when making a right turn on a curve, if coordinates are set on vertical and horizontal axes relative to gravity of earth as shown in FIG. 23A, the vehicle rolls to the left, and a head of the driver inclines to the right against a turning lateral acceleration. If the driver sees the scenery relative to the head coordinates at that time, the forward visibility rolls at an angle equal to or greater than a roll of the vehicle as shown in FIG. 23B.
At that time, the driver adjusts a head inclination angle so that a vector sum of acceleration of gravity and a turning lateral acceleration is directed into a direction near a head vertical axis. However, it is found that this position is not always stabilized and is varied. As a result of this variation, the driver's posture becomes unstable and with this, steering operation is disturbed, and this causes a vicious circle that this steering disturbance varies the turning lateral acceleration and the head inclination angle becomes further unstable.
The present inventors found that one of causes of sway of the head inclination angle is directional property of a window frame lower end line of the vehicle. That is, it is known that when one losses a horizontal degree of a reference line, he or she losses sense of balance. The present inventors have applied this to a vehicle and studied on this. As a result, it is confirmed that the sway of the window frame lower end line at the time of rolling visually disturbs the sense of balance and affects the head inclination angle.
Thereupon, the present invention has been accomplished while paying attention to the sense of balance of human, and the invention provides a visibility adjusting method and a visibility adjusting apparatus that can stabilize a sense of balance of a driver and suppress the sway of the head inclination angle by forming the parting line of the visibility adjusting section into a shape which is deviated from a straight line shape which can be seen as horizontal when running straightly, or by changing the parting line in accordance with turning condition such as a roll angle of a vehicle body.